Hi. About two years ago i decided to build a coop. We had contractors at our house so i asked them to clear the surface area. They convinced me that the floor surface of the run should be concrete to make ut easier to clean- but it just seems ti have complicated everything because nothing drains! Everything seems to get wet and stinky. I have covered the top of the run with plastic to stop the rain adding to it. I cover the concrete with sand. Its helped, but hasnt solved the issue. Do you have any suggestions?